A projection device that uses a digital micro-mirror device (hereinafter DMD) to modulate light from a light source has the advantage of providing bright images with high resolution. A DMD is an image display device in which micro-mirrors are arranged in an array, usually a two-dimensional array, with each mirror capable of being individually switched between two orientations so that it is either Off or On with regard to reflecting light from a light source towards an output aperture. Usually, light that is to be projected is reflected towards the output aperture by a micro-mirror in its On-position, and light that is not to be projected is reflected to a light absorbing body by the micro-mirror in its Off-position. The output aperture is usually the pupil of a projection lens.
When using a DMD to input image information onto a light beam, however, a problem sometimes occurs in that undesired light (hereinafter termed xe2x80x9cghost lightxe2x80x9d) may appear on the projection screen. More specifically, as one example, when an image is projected having a light color in the upper right area of the image field and a dark background, in some cases ghost light may appear in the lower right area of the screen. The area where the ghost light appears varies according to the structure of the device. Often, the ghost light will be incident onto the screen at an angle of about xc2x145xc2x0 to the normal of the screen surface. It is assumed that ghost light is formed by light that is undesirably reflected by one or more surfaces of the projection lens, re-enters the DMD, and is reflected by micro-mirrors which are in the Off-position (i.e., by Off elements) in a direction which causes the reflected rays to re-enter the projection lens and be projected onto the screen.
The present invention relates to a projection device having a projection lens for projecting fine details of an image, and that uses a DMD to modulate light from a light source with image information so as to create an image that is then projected onto a screen for observation. The object of the present invention is to prevent artifacts, caused by light which undesirably reflects from a surface of the projection lens and re-enters the DMD where it is again reflected toward the screen, from appearing on the screen in a noticeable manner.